Polyamide resin composition and molding thereof

ABSTRACT

A polyamide resin composition having good molding fluidity, heat and chemical resistance and dimensional stability is provided containing: (A) 30-90 weight percent, based on components (A) and (B), of a polyamide resin containing (i) 10-99 weight percent, based on components (i) and (ii) of an aromatic polyamide containing a carboxylic acid component derived from terephthalic acid or a mixture of terephthalic and isophthalic acid in which the isophthalic acid constitutes 40 mole percent or less of the mixture, and an aliphatic diamine component derived from a mixture of hexamethylene diamine and 2-methylpentamethylene diamine; and (ii) 1-90 weight percent, based on components (i) and (ii), of at least one polyamide selected from the group consisting of polyamides containing repeat units derived from alipathic dicarboxylic acids and alipathic diamines and polyamides containing repeat units derived from aliphatic aminocarboxylic acids; and (B) 10-70 weight percent, based on components (A) and (B), of an inorganic filler.

BACKGROUND OF THE INVENTION

This invention relates to polyamide resin compositions and a type ofpolyamide resin molding, characterized by the fact that the molding ismade of a polyamide resin composition with excellent fluidity during themolding process, and it has excellent mechanical characteristics, heatresistance, chemical resistance and dimensional stability when moistureis absorbed, so that it has a wide range of applications, includingparts used in automobiles, electrical/electronic parts, and furniture.

Conventional polyamide resins, such as nylon 66, nylon 6, nylon 612,etc., are aliphatic polyamide resins with a certain level of heatresistance and excellent mechanical characteristics. Consequently, theseresins are used in a wide range of applications, such as resin moldingsas substitutes for metal parts and resin moldings as substitutes for theparts made of heat-setting resins. However, in some applications, whenmoisture is absorbed, nylon 6 and nylon 66 exhibit characteristicdimensional changes. Also, stress cracks may take place due tochemicals.

In order to improve the chemical resistance, in particular, theresistance against calcium chloride, and other inorganic salts, forthese nylons, nylon 612 or a mixture of nylon 612 and nylon 66 hasconventionally been used. However, for the aforementioned mixture, theheat resistance drops due to the presence of nylon 612. This is adisadvantage.

In various applications, different problems exist with currentmaterials.

In the furniture field, glass-fiber-reinforced nylon 66 is widely usedin place of conventional metal parts in manufacturing chairs and otherarticles of furniture used in offices and homes. However, for theaforementioned glass-fiber-reinforced nylon 66, dimensional variationand degradation in properties take place due to moisture absorption.

Additionally, nylon 6 is also used to mold furniture parts to ensuregood appearance of the moldings. However, in the case of moistureabsorption, dimensional variation and degradation in properties becomeeven more significant when nylon 6 is used.

For the outer parts of electrical products, such as rice cookers, irons,and other home appliances, as well as word processors and other officeautomation equipment, superior mechanical characteristics such as theability to withstand high application temperatures, high resistanceagainst hydrolysis and high heat resistance to the high temperaturesapplied on the products during soldering are required. Also, theappearance of the moldings should be good for some products. However,for the moldings made of the conventional polyamide resin compositionsand polyester resin compositions, it is difficult to fully meet theaforementioned requirements.

As parts of electrical/electronic products, such as sealants forconnectors, coil bobbins, coils, etc., it is possible to make use ofpolyamide resin compositions and polyester resin compositions. For thesesealants, in addition to the high solder heat resistance, the partsshould have a small thickness in order to reduce the weight of theparts. As nylon 66 has good fluidity, it is able to flow through thenarrow gaps in the molding dies, so that thin-wall moldings can beformed. On the contrary, the solder heat resistance is poor. This is adisadvantage.

Regarding automotive applications, polyamide resins, in particular,reinforced polyamide resins, are used in manufacturing engine covers,parts connected directly to the engine covers, such as connectors, airintake manifolds, and other engine body parts, radiator tanks, caps, andother cooling system parts, canisters, pipelines, pump parts and otherfuel system parts. They are also widely used in manufacturing thegeneral connectors, relay boxes, gears, clips, etc., at present. Inparticular, nylon 66 is an appropriate type of material for theaforementioned applications, as it has excellent heat resistance,moldability and toughness. However, as pointed out above, when theaforementioned materials are used, variations in dimensions andproperties take place as moisture is absorbed. Consequently, it isnecessary to predict these variations and to take the appropriatemeasures in designing the parts. Consequently, their applications arelimited, and they are inappropriate for manufacturing high-precisionparts.

In addition to the aforementioned problems, there has recently been ahigh demand for reducing the size and increasing the power of automobileengines. Consequently, the requirement on the heat resistance of theresin products used in the engine room becomes higher and higher. Whenthis requirement is demanded, nylon 66 may be inappropriate in somecases.

For resin materials that are used to solve the aforementioned problemsand when moldings are to be made for relatively large-sized parts ofautomobiles, such as engine covers, radiator tanks, caps, air intakemanifolds, etc., fluidity like that of nylon 66 is required. Also, forthe aforementioned parts of automobiles, the resistance to various kindsof oil and chemicals should be high. Conventionally, nylon 66 and nylon6 are widely used, as they have high resistance against lubricants andactivating oils. On the other hand, in applications related to long-lifecoolant (referred to as LLC hereinafter), such as radiator tanks,reservoir tanks, heater cores, and other parts of the cooling system,the resistance to LLC also should be high, depending on the applicationenvironment. In addition, in recent years, due to the code inprohibiting studded tires, the frequency of contact between theautomobile parts with calcium chloride, calcium/magnesium acetate, andother snow-melting agents has been increased. When moldings made ofnylon 66 and nylon 6 come into contact with the aforementioned inorganicsalts under the prescribed conditions, stress cracks are sometimesgenerated, and it might be impossible to maintain the performance of themoldings.

In order to improve the chemical resistance of the aforementionedresins, conventionally, nylon 612, nylon 810, nylon 11, nylon 12 andother long-chain aliphatic polyamides have been used either directly oras mixtures with nylon 66. However, these materials have heatresistances lower than that of nylon 66. This is a disadvantage.

Japanese Kohyo Patent No. Hei 5 1993!-506871 discloses a type ofcopolymer made of aromatic polyamide consisting of terephthalic acidcomponent units and diamine component units of hexamethylenediamine and2-methylpentamethylenediamine. However, when the aforementioned aromaticpolyamide is used in manufacturing automobile engine covers, air intakemanifolds, radiator tanks, and other automobile parts, the legs ofoffice chairs, and other relatively large furniture parts, relativelythin-walled parts and housings, and other electrical/electronic parts,etc., the fluidity of the resin is poor in the molding operation.

Based on the foregoing discussion, a purpose of this invention is toprovide a type of polyamide resin composition with excellent fluidity inthe molding operation. Another purpose is to provide a type of polyamideresin molding with excellent mechanical characteristics, heatresistance, chemical resistance and dimensional stability upon moistureabsorption for use in a wide range of applications, includingelectrical/electronic applications, furniture applications, andautomotive applications.

SUMMARY OF THE INVENTION

In order to realize the aforementioned purposes, the present inventionprovides a type of polyamide resin composition which comprises:

(A) 30-90 weight percent, based on components (A) and (B), of apolyamide resin containing

(i) 10-99 weight percent, based on components (i) and (ii) of anaromatic polyamide containing a carboxylic acid component derived fromterephthalic acid or a mixture of terephthalic and isophthalic acid inwhich the isophthalic acid constitutes 40 mole percent or less of themixture, and an aliphatic diamine component derived from a mixture ofhexamethylene diamine and 2-methylpentamethylene diamine; and

(ii) 1-90 weight percent, based on components (i) and (ii), of at leastone polyamide selected from the group consisting of polyamidescontaining repeat units derived from aliphatic dicarboxylic acids andaliphatic diamines and polyamides containing repeat units derived fromaliphatic aminocarboxylic acids; and

(B) 10-70 weight percent, based on components (A) and (B), of aninorganic filler.

The polyamide resin composition of this invention has excellent fluidityduring molding. Consequently, molding can be carried out easily forlarge-sized parts, small-sized parts and thin-walled parts. The moldingsexhibit excellent mechanical characteristics, heat resistance, chemicalresistance and dimensional stability. Consequently, they can be used notonly in the field of automobiles, electrical/ electronic parts andfurniture, but also in the other fields. In particular, the polyamideresin composition moldings of this invention have all of the requiredcharacteristics for under-the-hood parts of automobiles, and they can beused for a long period of time.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a type of polyamide resin compositionwhich comprises:

(A) 30-90 weight percent, based on components (A) and (B), of apolyamide resin containing

(i) 10-99 weight percent, based on components (i) and (ii) of anaromatic polyamide containing a carboxylic acid component derived fromterephthalic acid or a mixture of terephthalic and isophthalic acid inwhich the isophthalic acid constitutes 40 mole percent or less of themixture, and an aliphatic diamine component derived from a mixture ofhexamethylene diamine and 2-methylpentamethylene diamine; and

(ii) 1-90 weight percent, based on components (i) and (ii), of at leastone polyamide selected from the group consisting of polyamidescontaining repeat units derived from aliphatic dicarboxylic acids andaliphatic diamines and polyamides containing repeat units derived fromaliphatic aminocarboxylic acids; and

(B) 10-70 weight percent, based on components (A) and (B), of aninorganic filler.

In present invention, the aromatic polyamide defined in (A)(i) has anintrinsic viscosity in sulfuric acid at 25° C. in the range of 0.2-3.0.Also, the melting point is in the range of 280°-330° C. The mixture ofhexamethylene diamine and 2-methylpentamethylene diamine preferablycontains 40-90 mole percent, based on the mixture, of hexamethylenediamine. This aromatic polyamide can be manufactured by means ofpolycondensation well known by those persons skilled in the art.

The polyamide defined in (A)(ii) is basically used for adjusting thefluidity of the polyamide resin composition of this invention accordingto the intended application of use. Examples of the polyamide defined in(A)(ii) include nylon 66, nylon 6, nylon 612, nylon 46, nylon 11, nylon12 and other aliphatic polyamides. When these aliphatic polyamides areblended with the aforementioned aromatic polyamide to form the polyamideresin of component (A), it is possible to adjust the fluidity in moldingoperation.

As far as the blending method is concerned, it is possible to use abiaxial extruder to perform melting/blending of the polyamides, or toblend two types of polyamides in pellet form before molding.

Also, it is possible to obtain a polymer with the desired molecularweight by the polymerization of low-molecular substances that form thevarious polyamides or of a mixture of the various polyamides and thelow-molecular substances that form the polyamides.

Also, it is possible to manufacture the aforementioned polyamide resinby means of polycondensation of terephthalic acid alone or its mixturewith isophthalic acid, adipic acid, hexamethylenediamine, and2-methylpentamethylenediamine. The polyamide resin prepared in theaforementioned process of polymerization/blending or blending is thenused for injection molding or extrusion molding to form the moldingproduct.

The amount of the aforementioned aliphatic polyamide should be in therange of 1-90 weight percent, or preferably in the range of 5-85 weightpercent, based on the total of aromatic and aliphatic polyamides.

When the amount of the aromatic polyamide in the polyamide resin is lessthan 10 weight percent, it is difficult to find the difference betweenthe polyamide resin composition and nylon 66 or other aliphaticpolyamide with respect to the heat resistance and dimensional stability,and the effect of adding the aforementioned aromatic polyamide becomesinsignificant. For example, for automotive parts, the improvements inheat resistance and the resistance to calcium chloride areinsignificant. Also, for parts of furniture, there is no significantimprovement in the variation of dimensions caused by moistureabsorption.

The amount of the aforementioned aliphatic polyamide in the polyamideresin should be determined appropriately according to the type and sizeof the molded part. When relatively large-sized parts, such as enginecovers, air intake manifolds, radiator tanks, etc., are manufactured,the fluidity of the resin should be high in the molding operation.Consequently, in this case, the amount should be larger than that in thecase of small-sized parts. Even when small parts are manufactured, ifthe application is for thin-wall connectors, sealants, etc., a highfluidity of the resin during molding is still required. Consequently, anappropriate amount of aliphatic polyamide should be added into thepolyamide resin.

Further, for the polyamide resin composition of this invention, theamount of the inorganic filler added should be in the range of 10-70weight percent, or preferably in the range of 15-60 weight percent,based on the polyamide resin and the inorganic filler. Examples ofinorganic fillers that can be used include glass fibers, carbon fibers,calcium titanate, whiskers, kaolin, talc, mica, etc. If it is necessaryto increase the mechanical strength of the molding, it is preferable toadd glass fibers. If it is necessary to increase the dimensionalstability of the molding and to suppress warpage, kaolin, talc, mica orglass flakes may be added. If the amount of the inorganic filler is lessthan 10 weight percent, the mechanical characteristics desired in manyapplications cannot be obtained for the molded part.

In addition, for the polyamide resin composition of this invention, aslong as the characteristics of the obtained molding are not degraded,other additives, such as thermal stabilizers, plastizers, oxidationinhibitors, dyes, pigments, mold-release agents, etc., may be added inappropriate amounts in addition to the aforementioned aromaticpolyamide, aliphatic polyamide, and inorganic filler.

For preparing the moldings of the present invention, variousconventional molding methods may be adopted, such as compressionmolding, injection molding, blow molding and extrusion molding. Also,depending on the demand, it is possible to post process the molding toform the product.

EXAMPLES

In the following, this invention will be explained in more detail withreference to application examples.

Application Examples 1-4 and Comparative Examples 1-3

The various components listed in Table I were melt-blended in a biaxialextruder (TEM35, made by Toshiba). After cooling by water, pellets weremanufactured. The obtained pellets were used to mold specimens measuring13 mm×130 mm×3.2 mm according to ASTM D838. The obtained specimens wereused to measure the mechanical characteristics. The measurements weremade according to the following test methods.

(1) Tensile Strength: ASTM D638

(2) Elongation: ASTM D638

(3) Flexural Modulus: ASTM D790

(4) Flexural Strength: ASTM D790

(5) Notched Izod: ASTM D256

(6) Load Warpage Temperature: ASTM D648

(7) Resistance to Calcium Chloride: Under stress of 200 kg/ cm²,saturated solution of calcium chloride was coated at 23° C. and thendried at 100° C. for 2 hours. This operation was then repeated, and thecondition of the surface of the specimen was observed.

(8) LLC Resistance: The specimen was dipped for 100 hours in 50% aqueoussolution of ethylene glycol at 120° C., followed by setting at roomtemperature, and then a tensile test was carried out according to themethod disclosed in (1). In this case, the result was compared with thetensile strength measured right after molding.

(9) Appearance: The surface gloss of a plate molding measuring 75 mm×100mm×3.2 mm was inspected visually and was rated according to a 3-valuerating system. Excellent surface gloss was assigned a value of 1; goodsurface gloss was assigned a value of 2; and poor surface gloss wasassigned a value of 3.

(10) Change in Dimensions: Immediately after a plate measuring 75 mm×100mm×3.2 mm was molded, and then after it was saturated with water byabsorption at 50° C., the dimensions were measured, and the differencewas calculated.

(11) Fluidity: The spiral flow at a resin temperature of 310° C.,injection pressure of 800 kgf/cm² and a die temperature of 120° C. wasmeasured.

The aromatic polyamides used in Application Examples 1-4 were mixturesmade of terephthalic acid and hexamethylenediamine and2-methylpentamethylenediamine. The amount of hexamethylenediamine in thediamine component was 50 mol %, and the amount of2-methylpentamethylenediamine was also 50 mol %.

As nylon 66, an aliphatic polyamide listed in Table I, Zytel® 101,produced by E. I. du Pont de Nemours and Company, was used. As nylon612, Zytel® 151L, also manufactured by E. I. du Pont de Nemours andCompany was used. Also, as glass fibers, 10-μm chopped strandsmanufactured by Nippon Sheet Glass Co., Ltd., were used.

The results of tests (1)-(5) are listed in Table II, and the results oftests (6)-(11) are listed in Table III.

                  TABLE I                                                         ______________________________________                                                          Aromatic               Glass                                Application                                                                           Comparative                                                                             Polyamide                                                                              Nylon 66                                                                             Nylon 612                                                                            Fibers                               Example Example   (%)      (%)    (%)    (%)                                  ______________________________________                                        1                 22       45     --     33                                   2                 33       33     --     33                                   3                 45       22     --     33                                   4                 45       --     22     33                                           1         67       --     --     33                                           2         --       67     --     33                                           3         --       --     67     33                                   ______________________________________                                    

                                      TABLE II                                    __________________________________________________________________________                          Appli-                                                                             Appli-                                                                             Appli-                                                                             Compa-                                                                             Compa-                                                                             Compa-                                               cation                                                                             cation                                                                             cation                                                                             rative                                                                             rative                                                                             rative                              Temper-                                                                            Relative                                                                           Test   Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                        Property                                                                           ature                                                                              Humidity                                                                           Method                                                                            Units                                                                            1    2    3    1    2    3                              __________________________________________________________________________    Tensile                                                                             23° C.                                                                     50%  D638                                                                              (kgf/                                                                            2,090                                                                              2,250                                                                              2,220                                                                              2,310                                                                              1,900                                                                              1,690                          Strength                                                                            23° C.                                                                              cm.sup.2)                                                                        1,580                                                                              --   1,960                                                                              2,090                                                                              1,270                                                                              1,410                               120° C.   950  910  --   980  910  790                            Tensile                                                                             23° C.                                                                     50%  D638                                                                              (%)                                                                              2.6  2.4  2.5  2.6  3    5                              Breaking                                                                            23° C.   3.9  --   2.6  2.2  4    5                              Elongation                                                                         120° C.   7.8  7.5  --   3.8  7    9                              Flexural                                                                            23° C.                                                                     50%  D790                                                                              (kgf/                                                                            3,040                                                                              3,070                                                                              3,000                                                                              3,210                                                                              2,670                                                                              2,600                          Strength                                                                            23° C.                                                                              cm.sup.2)                                                                        2,430                                                                              --   2,800                                                                              2,878                                                                              2,100                                                                              1,700                               120° C.   1,330                                                                              1,360                                                                              --   1,900                                                                              1,400                                                                              1,000                          Flexural                                                                            23° C.                                                                     50%  D790                                                                              (kgf/                                                                            108,500                                                                            117,800                                                                            110,900                                                                            115,300                                                                            91,400                                                                             84,400                         Modulus                                                                             23° C.                                                                              cm.sup.2)                                                                        86,000                                                                             --   109,900                                                                            116,400                                                                            63,300                                                                             62,400                              120° C.   47,900                                                                             48,700                                                                             --   87,390                                                                             42,800                                                                             36,000                         Notched                                                                             23° C.                                                                     50%  D256                                                                              (kgf/                                                                            10   11   10   11   11   14                             Izod  23° C.                                                                              cm.sup.2)                                                                        10   10   10   10   14   14                             Impact                                                                        Load  23° C.                                                                     50%  D648                                                                              (°C.)                                                                     244  245  --   262  249  212                            Warpage                                                                             23° C.                                                           Tempera-                                                                      ture                                                                          __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________                    % Change in                                                                           Calcium Chloride                                                      Dimensions Due                                                                        Resistance                                                                            % Retention of                                                to H.sub.2 O                                                                          (No. of Cycles                                                                        Tensile Fluidity                              Application                                                                         Comparative                                                                         Surface                                                                           Absorption at                                                                         Until   Strength                                                                              (Flow Length                          Example                                                                             Example                                                                             Gloss                                                                             100% RH Breaking)                                                                             (LLC Resistance)                                                                      in cm)                                __________________________________________________________________________    1           1   0.78            64      77                                    2           1   --      Not Broken                                                                            --      67                                                            (Crack Free)                                          3           3   0.65    Not Broken                                                                            82      57                                                            (Crack Free)                                          4           2   --      Not Broken                                                                            --      99                                                            (Crack Free)                                                1     2   0.65    Not Broken                                                                            89      35                                                            (Crack Free)                                                2     2   1.16    7       53      94                                          3     1   0.43    Not Broken                                                                            63      >120                                                          (Crack Free)                                          __________________________________________________________________________

As can be seen from Table II, the resin compositions in ApplicationExamples 1-4 have mechanical characteristics superior to those of theresin composition in Comparative Example 2. As can be seen from TableIII, when the resin compositions in Application Examples 1-4 werecompared with Comparative Example 1, the fluidity in molding wasimproved by adding nylon 66 or nylon 612. When the moldings of resincompositions in Application Examples 1-4 were compared with those inComparative Examples 2 and 3, there was better retention of mechanicalproperties (i.e., tensile strength). When the moldings made of the resincompositions in Application Examples 1-4 were compared with that inComparative Example 2, the resistance to calcium chloride was improvedsignificantly and dimensional stability was improved as well.

I claim:
 1. A polyamide resin composition comprising:(A) 30-90 weightpercent, based on components (A) and (B), of a polyamide resincontaining(i) 10-99 weight percent, based on components (i) and (ii) ofan aromatic polyamide containing a carboxylic acid component derivedfrom terephthalic acid or a mixture of terephthalic and isophthalic acidin which the isophthalic acid constitutes 40 mole percent or less of themixture, and an aliphatic diamine component derived from a mixture ofhexamethylene diamine and 2-methylpentamethylene diamine; and (ii) 1-90weight percent, based on components (i) and (ii), of at least onepolyamide selected from the group consisting of polyamides containingrepeat units derived from aliphatic dicarboxylic acids and aliphaticdiamines and polyamides containing repeat units derived from aliphaticaminocarboxylic acids; and (B) 10-70 weight percent, based on components(A) and (B), of an inorganic filler.
 2. A polyamide resin composition asrecited in claim 1, wherein the mixture of hexamethylene diamine and2-methylpentamethylene diamine of component (i) contains 40-90 molepercent, based on said mixture, of hexamethylene diamine.
 3. An articlemolded from a polyamide resin composition as recited in claim
 1. 4. Anarticle as recited in claim 3 for use in electrical or electronicapplications.
 5. An article as recited in claim 3 for use in automotiveapplications.
 6. An article as recited in claim 3 for use in furnitureapplications.